A conventional manual shift transmission contains one clutch that is normally closed, or applied, by a spring. It is manually disengaged by the driver to shift gears. With a conventional manual transmission, operating the clutch and shifting the gears must be performed in sequence. To shift gears, the driver reduces the engine throttle, and pushes the clutch pedal to release the clutch. With the clutch released, the driver manually shifts to another gear, and then reapplies the clutch and throttle.
A dual clutch transmission of a vehicle typically utilizes two manual shift transmissions in a single housing to drive the wheels of a vehicle with different gear ratios or stages. A conventional dual clutch transmission generally contains two independent clutches that are normally open or released, and further includes at least one input shaft, and at least one output shaft operatively coupled with each other. Each of the two clutches is coupled to its corresponding input shaft to drive an output shaft with a selected gear ratio among multiple gears. In order to perform the gear shifting process, the dual clutch transmission typically also includes a gear shift actuating device which is driven by one or more actuators.
For example, the present invention (as will be described below in detail) discloses a dual clutch transmission having two independent clutches coupled with multiple gears, namely, six forward gears and one reverse gear in the exemplary embodiment disclosed. According to this embodiment, a first clutch (to be referred below either a first clutch or “A” clutch) drives the odd numbered gears, namely, the first, third, and fifth gears, and a second clutch (to be referred below either a second clutch or “B” clutch) drives the even numbered gears, namely, the second, fourth, and sixth gears, plus the reverse gear.
With a dual clutch transmission, operating the clutches is separated from shifting the gears. The normally open clutches of the dual clutch transmission allow “pre-selecting” which is the ability to engage one gear while another gear is driving. Pre-selecting provides a very fast shift because there is no time lost by releasing the clutch, shifting to the next gear, and then applying the clutch as in the manual shift transmissions.
For example, when starting the vehicle, the transmission is in the first gear with the first clutch (“A” clutch) applied, and the second clutch (“B” clutch) released. To shift into the second gear, the shifter pre-selects the second gear, which is idle. The “A” clutch is then released, and the “B” clutch is applied. This clutch to clutch shift takes place in about 0.5 second. First gear is then disengaged.
To continue the sequence and shift to the third gear, the third gear is pre-selected. Then the “B” clutch is released, and the “A” clutch is applied. The second gear is then disengaged. This shifting sequence proceeds, automatically, up to the sixth gear.
The clutches are alternately applied and released by electro-mechanical actuators that are controlled by an on-board computer. If the clutch and actuator systems are properly designed, the shifts of the dual clutch transmission simulate the smooth shift of an automatic transmission.
In order to accurately control the application and release of the two clutches, they must be free to operate independently. Any interference between the two clutches could result in unpredictable operation. In addition, the normally open dual clutches will ‘fail safe”. When the engine is shut off, or if electrical power is lost, the low friction of the actuators allow the internal clutch springs to release the clutches automatically.
Smooth shifts in a conventional manual transmission are a function of the driver's skill in operating the clutch. If the clutch is applied too quickly, the shift will be harsh, and may stall the engine at low speeds. If the shift is too slow, vehicle acceleration and clutch life will be degraded.
The shifts with the dual clutch transmission are independent of operator skill, similar to an automatic transmission. The computer applies one clutch while releasing the other. If one clutch applies before the other releases, the engine must drive two gears at once, which reduces acceleration. This is called overlap. If both clutches are released at the same time, the engine speed will suddenly increase, or flare.
Conventional dual clutch actuators appear to concentrate on the carefully controlled clutch application, but almost ignore the release function. The typical slow release of conventional designs almost guarantees overlap.
The ideal shift control will regulate the torque capacity of both clutches so the sum of both clutches is 100% of engine torque. During shifting, one clutch must transition from 100% engaged to 100% released, at the same time as the other clutch is transitioning from 100% released, to 100% engaged. An overlap will occur if the sum of the torque capacity of both clutches exceeds 100%. A flare will occur if the torque sum of both clutches is less than 100%.
With conventional actuators, shift timing becomes critical to both shift feel and clutch life. Many suggestions have been introduced to improve the shift timing of the dual clutch transmission, since poor shifting is the main driver's complaint about dual clutch transmissions.
In an automatic transmission, the best quality shift transfers power from a one way, or overrunning, clutch (ORC) to another shift element. As the name implies, an ORC locks in one direction, and freewheels in the other direction. If it is designed to lock in the clockwise direction, it will unlock when rotated in the counter clockwise direction. An ORC releases instantly when the direction of rotation of reverses. Since it cannot release until another shift element takes the load, there can be no overlap or flare. Therefore, the ORC eliminates shift timing problems.
Dual clutch transmissions cannot use an ORC because the clutches must be capable of driving in both directions. However, a very fast clutch release mechanism should mimic the instant release of the ORC. With a fast release, shift timing problems should be minimized or eliminated.
The present invention is designed to address or solve at least some of the above described drawbacks and other problems of the dual clutch transmission known in the art, for example, slow clutch release and poor shift timing problems. The present invention provides a new dual clutch transmission with reliable construction and enhanced clutch shift operation. In addition, the dual clutch transmission of the present invention incorporates an effective and space-efficient design with its two clutches arranged in the same direction with its two clutch-actuating devices, and also with its gear shifting device coupled thereto for gear shift operation. Accordingly, the size and volume of the transmission can be reduced compared to a conventional dual clutch transmission.
Moreover, the dual clutch transmission of the present can provide a fast clutch release operation compared to the conventional dual clutch transmission, as is further described below.
Conventional clutches use a diaphragm spring that is similar to a Belleville spring, to transmit force from the thrust bearing to the clutch pressure plate. To release the conventional, normally closed clutch, the thrust bearing applies a load to the diaphragm spring. This thrust is transferred through the clutch assembly to the engine thrust bearings. Since this load is only applied for a short time, it does not damage the engine bearings. The diaphragm spring also acts as a lever to multiply the thrust bearing force by two to three times. However, the diaphragm spring has a large amount of hysteresis. The force and travel at the pressure plate are non-linear as compared to the thrust bearing force. Because of hysteresis, the spring maintains a residual force on the pressure plate, after the thrust bearing has been partially retracted. The spring must travel a considerable distance before all force on the pressure plate is removed. This residual force contributes to overlap, when the clutch is not fully released.
As will be described below in detail, the clutch design of the present invention replaces the diaphragm spring with stiff levers that have no hysteresis. Therefore, the relationship between the thrust bearing travel and the pressure plate travel is linear. When the apply force is removed, the pressure plate force is released instantly.
Moreover, as will also be described below in detail, the clutch design of the present invention utilizes a positive release mechanism unlike the conventional clutch design having only a diaphragm spring for the release operation.
Conventional clutch actuators are designed to transmit force to the thrust bearing in the apply direction only. They rely on the diaphragm spring to retract the thrust bearing and actuator to the fully released position. The conventional design, combined with the diaphragm spring hysteresis could result in uncontrolled operation. This may also explain the difficulty in controlling the clutch overlap, mentioned above.
The clutch actuator system of the present invention is designed to transmit force to the thrust bearing in both directions, apply and release. This design allows a complete control of both the application and release functions.
The clutch actuator of the present invention consists of a small electric motor and planetary gear set to rotate a ball screw. The ball screw nut moves the clutch apply bearing through a lever. The motors contain small brakes to hold position so the motor power may be turned off when the desired thrust bearing load has been achieved. Both actuators operate independently, and are designed to apply or release the driving clutch in milliseconds. The application and release speed can be modulated for throttle conditions. For example, when the vehicle is accelerating rapidly, with a high throttle opening, the engaging clutch will apply quickly. With low throttle openings, the clutch apply is slowed for a smoother shift.
Other special features, characteristics, and improvements of the present invention over the conventional dual clutch transmission system and its actuation devices and dual clutch assembly thereof, will be further described below or otherwise can be recognized from the entire disclosure of this invention by the person skilled in the art.
According to one aspect of the invention, the dual clutch transmission with multiple gears operatively coupled thereto, comprises:
a first input shaft and a second input shaft, the first and second input shafts disposed coaxially to each other and operatively coupled with a plurality of gears and at least one output shaft to drive the transmission with a selected one from the plurality of gears;
a first clutch of generally annular shape, which is operatively coupled with one of the first and second input shafts to drive the transmission with a gear selected from a first set of non-consecutively numbered gears;
a second clutch of generally annular shape, which is disposed coaxially with the first clutch and operatively coupled with the other one of the first and second input shafts to drive the transmission with a gear selected from a second set of non-consecutively numbered gears;
a first clutch actuating device and a second clutch actuating device, each of the first and second clutch actuating devices including an actuator and a pivot member, each pivot member of the first and second clutch actuating devices having a first end operatively coupled to the actuator and a second end operatively coupled to a clutch applicator, each clutch applicator of the first and second clutching actuating devices having a cylindrical shape, each pivot member of the first and second clutching actuating devices configured to pivotally move about a center of pivot to move its clutch applicator for clutch operation; and
a plurality of first and second clutch levers received in a clutch retaining housing in a circularly arranged pattern, the first clutch levers operatively coupled between the first clutch and the clutch applicator of the first clutch actuating device, the second clutch levers operatively coupled between the second clutch and the clutch applicator of the second clutch actuating device;
wherein the cylindrically shaped clutch applicator of the first clutch actuating device is disposed coaxially with the cylindrically shaped clutch applicator of the second clutch actuating device, and the first clutch levers and the second clutch levers are alternately arranged in the clutch retaining housing such that the first clutch levers and the second clutch levers can operate independently to each other upon movement of the first clutch applicator or the second clutch applicator to perform a selective clutch operation between the first and second clutches.
In one preferred embodiment, the dual clutch transmission includes six gears plus one reverse gear, and one of the first and second clutches is configured to operate the first, third, and fifth gears, and the other one of the first and second clutches is configured to operate the second, fourth, sixth gears, and the reverse gear.
In another preferred embodiment, the clutch retaining housing includes a first housing member at a first side of the clutch retaining housing, and a second housing member at a second side of the clutch retaining housing, and wherein a majority of components of the second clutch are disposed in the clutch retaining housing near to the first housing member, and a majority of components of the first clutch are disposed in the clutch housing near to the second housing member. The second clutch preferably includes a second clutch application plate of generally annular shape which is coupled with the second clutch levers for the operation of the second clutch, a friction plate arranged next to the second clutch application plate and coupled with a hub of the second clutch, the hub of the second clutch coupled with the second input shaft, and a reaction plate arranged next to the friction plate. The first clutch preferably includes a clutch finger plate of generally annular shape, the clutch finger plate having a plurality of fingers extending in the axial direction of the first clutch and through an outer circumference of the second clutch and configured to push a first clutch application plate of generally annular shape which is coupled with the first clutch levers for clutch application of the first clutch, and a friction plate arranged next to the first clutch application plate and coupled with a hub of the first clutch, the hub of the first clutch coupled with the first input shaft.
In another preferred embodiment, the first and second clutch application plates are coupled with at least one plate spring, respectively, for release operation of the clutches.
According to another aspect of the invention, the clutch actuation apparatus for a dual clutch transmission having first and second clutches coaxially arranged to each other, comprises:
a first clutch actuating device and a second clutch actuating device, each of the first and second clutch actuating devices including an actuator and a pivot member, each pivot member of the first and second clutch actuating devices having a first end operatively coupled to the actuator and a second end operatively coupled to a clutch applicator, each clutch applicator of the first and second clutch actuating devices having a cylindrical shape, the cylindrically shaped clutch applicator of the first clutch actuating device disposed coaxially with the cylindrically shaped clutch applicator of the second clutch actuating device, each pivot member of the first and second clutch actuating devices configured to pivotally move about a pivot to move its clutch applicator for operation of the first and second clutches.
According to another aspect of the invention, the dual clutch apparatus for a dual clutch transmission having first and second input shafts disposed coaxially to each other and operatively coupled with a plurality of gears, comprises:
a first clutch of generally annular shape, which is operatively coupled with one of the first and second input shafts to drive the transmission with a gear selected from a first set of non-consecutively numbered gears;
a second clutch of generally annular shape, which is disposed coaxially with the first clutch and operatively coupled with the other one of the first and second input shafts to drive the transmission with a gear selected from a second set of non-consecutively numbered gears; and
a plurality of first and second clutch levers received in a clutch retaining housing in a circularly arranged pattern with the first clutch levers alternately interleaved with the second clutch levers;
wherein the second clutch includes a second clutch application plate of generally annular shape which is coupled with the second clutch levers for operation of the second clutch, a friction plate arranged next to the second clutch application plate and coupled with a hub of the second clutch, the hub of the second clutch coupled with the second input shaft, and a reaction plate arranged next to the friction plate;
wherein the first clutch includes a clutch finger plate of generally annular shape, the clutch finger plate having a plurality of fingers extending in the axial direction of the first clutch and through an outer circumference of the second clutch and configured to push a first clutch application plate of generally annular shape which is coupled with the first clutch levers for clutch application of the first clutch, and a friction plate arranged next to the first clutch application plate and coupled with a hub of the first clutch, the hub of the first clutch coupled with the first input shaft.